horse chestnut

noun

1.

any of several trees of the genus Aesculus, esp the Eurasian A. hippocastanum, having palmate leaves, erect clusters of white, pink, or red flowers, and brown shiny inedible nuts enclosed in a spiky bur: family Hippocastanaceae

2.

Also called conker. the nut of this tree

Word Origin

C16: so called from its having been used in the treatment of respiratory disease in horses